The present invention generally relates to insulated containers, and more specifically relates to insulated containers having refrigeration units.
Insulated containers, also called xe2x80x9ccoolers,xe2x80x9d are prevalent in contemporary life. The insulated containers are often used for picnics or for outdoor activities such as camping or sporting events. In addition, insulated containers are becoming more prevalent in the medical industry, where they are used to move transplant organs and other articles that need to remain cold during transport. Also, the need to transport commercial goods such as perishable food, drink, medicine, and environmental samples is becoming more important.
One downside to current insulated containers is that the length of time that an insulated container can keep something cold is limited. For example, if ice is used in the insulated container, the ice will often melt because the cooler cannot maintain the colder interior temperatures needed to prevent melting of the ice. Frozen ice packs do not last much longer. Traditional vapor cycle systems, while efficient, are quite large and heavy. Most of these systems require a 110-volt outlet to operate. A few 12 volt or 24 volt systems are available today; however, these systems are also large and heavy. The vapor cycle 12 and 24-volt systems also may have problems with vibrations during transportation. In addition, there exists absorption and adsorption refrigerators, but these fail if enough vibrations exist and improper orientation may also cause the units to fail. Like the vapor cycle refrigerators, these cooler systems are heavy, and must use ammonia in order to freeze.
Another downside to insulated containers is that they often cannot be maintained at freezing temperatures for very long. To solve this problem, many companies often use dry ice to keep the contents of an insulated container cold. However, even dry ice has time limitations, and its use and handling is difficult.
One solution that has recently been used for providing insulated containers that can maintain cold temperatures for long periods of time is to provide refrigeration units as components of the insulated containers. Such refrigeration units typically must be plugged into an AC outlet or a car cigarette lighter to provide cooling. While such a cooling unit works well for cooling items in the insulated container, an AC outlet or similar power supply is not always readily available.
The present invention provides an insulated container utilizing Stirling cooler technology. In accordance with one aspect of the present invention, the insulated container and the Stirling cooler include a self-contained, portable power source associated with them. For example, the portable power source may be a battery, a fuel cell, a flexible solar panel, a Stirling generator, or a combustion engine generator.
In accordance with another aspect of the present invention, the Stirling cooler may provide cooling to the insulated container in a number of different ways. As one example, a heat sink may be attached to a cold portion (i.e., heat acceptor portion) of the Stirling cooler and a fan may blow through the heat sink and into the insulated interior portion of the cooler, thus providing refrigeration. In another example, a heat pipe or a thermosyphon may be attached to the heat acceptor portion of the Stirling cooler and the working fluid of the thermosyphon (e.g., water) may be circulated from the heat acceptor of the Stirling cooler into the insulated container. In one embodiment, the heat pipe or thermosyphon is arranged as a series of coils on the inside of the compartment to be cooled, and the Stirling cooler is located on the outside of that compartment. In another embodiment, the heat pipe or the thermosyphon extends around a lower portion of the cooler, and includes a metal liner adjacent thereto. Alternatively, the heat pipe or thermosyphon may be arranged around a top portion of the cooler, with a metal liner adjacent thereto. The heat pipe may also be attached to a metal plate that is externally attached to the inner liner of a cooler then foamed into place. This method provides an insulated container having an interior that is easy to clean.
In accordance with another aspect of the present invention, if the heat sink and fan are used, the insulated container provides refrigeration only. However, if the heat pipe or thermosyphon is used, the cycling of the Stirling cooler may be increased so that the same insulated container may also be used simultaneously as a freezer. Controls may be provided that regulate the cycling of the Stirling cooler so that the internal temperature of the insulated container may be controlled. If desired, the cycling of the Stirling cooler may be changed so that the heat acceptor regulates temperature sufficiently to permit an insulated container having a heat pipe or a thermosyphon to be used alternatively as a refrigerator or a freezer.
In accordance with still another aspect of the present invention, an insulated container using the heat pipe or thermosyphon to provide a freezer portion may additionally include a separate chamber within the insulated container that provides refrigeration. In accordance with one aspect of this embodiment of the present invention, a small adjustable or fixed opening is provided between the freezer portion and the refrigerator portion. Cold air flows from the freezer portion into the refrigerator portion, providing sufficient cooling to provide refrigeration. Alternatively, instead of a small hole, insulation between the two compartments may be sufficiently thin such that thermal transfer is provided between the two containers. Still another compartment may be provided that is insulated from the freezer and/or refrigerator compartments and that is not refrigerated or cooled at all. Yet another insulated container may utilize heat from the hot portion (heat rejecter side) of the Stirling cooler for warming or heating a compartment.
In accordance with another aspect of the present invention, a heat sink is provided on the hot portion (heat rejecter side) of the Stirling cooler. This heat sink and the hot portion of the Stirling cooler may be mounted on the outside of the insulated container. If mounted inside, they are mounted in a separate compartment from the cooled compartment or compartments. A fan is provided for conducting heat away from the heat sink attached to the heat rejecter of the Stirling cooler. If mounted inside a compartment, a hole may be provided in the side of the cooler for permitting the hot air to flow out of the cooler.
The Stirling cooler of the present invention provides a portable refrigeration or freezing unit that requires very little energy input. The unit may provide heating, ambient, refrigeration, or freezing, or any combination thereof, each with a specific compartment. In addition, because the invention uses Stirling technology, the refrigeration unit is nonpolluting, quiet, lightweight, and efficient.